Kinetic Study and Optimization of Lactic Acid Production from Corncob

Adoga D. O., Samuel S. S., Egemba K. C., Ojong O. E.

Abstract


In this study, corncob, an agricultural waste, was utilized in the production of lactic acid, the   process was optimized while the kinetics of the process was also investigated. The corncob was hydrolyzed using diluted Sulphuric acid, followed by the fermentation of the hydrolysate by lactobacillus delbrueckii to produce lactic acid. Experimental design based on central composite design (CCD) was used for the fermentation steps, while Response surface methodology (RSM) was used for the optimization of the process. For the fermentation step, glucose concentration, reaction time, temperature and pH were the process variables. The results obtained from the lactic acid fermentation process were then fitted into kinetic models to establish the kinetics of the process. The statistical analysis also showed that the lactic acid yield of 72.1% was obtained at optimized variables of temperature of 42oC, pH of 5.6, reaction time of 120h and glucose concentration of 10g/l. An excellent correlation exists between the predicted yields and the experimental yields, the coefficient of determination (R2) given as 0.9654 indicates a well-fitted and reliable model. From the kinetic study of the lactic acid production process, there was an excellent fit to the first order kinetic model, this reveals a good agreement with the observed value of lactic acid yield (72.1%). Hence, useful kinetic parameters were determined based on the first order kinetic model. The values of the rate constant at 20oC, 30oC, 40oC, 50oC and 60oC are, 0.0026min-1; 0.0027min-1;0.0033min-1;0.042min-1and 0.004min-1 respectively The activation energy (Ea), needed for the conversion of corncob hydrolysate into lactic acid was found to be 12.79Kj/mol, while the pre-exponential factor was 2.145min-1 It is evident that corncob has the potentials, to produce high yield of lactic acid.             


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